In recent years, organic EL devices have been gathering attention as illumination devices that replace incandescent lamps or fluorescent lamps, and many studies are made thereon.
Here, an organic EL device is a device in which an organic EL element is stacked on a substrate such as a glass substrate or a transparent resin film. The organic EL element is an element in which two electrodes, one or both of which are translucent, oppose each other, and a light emitting layer made of an organic compound is stacked between the electrodes. The organic EL device emits light by using energy from recombination of electrically excited electrons and positive holes.
The organic EL device is a self-luminous device, and can emit light of various wavelengths by selecting the material of the light emitting layer as appropriate. Further, the organic EL device is extremely thin as compared to the incandescent lamp and the fluorescent lamp, and emits light in a planar manner. Therefore, the organic EL device is less restricted as to the installation place.
The representative layer structure of the organic EL device is as shown in FIG. 11. An organic EL device 200 shown in FIG. 11 has the structure referred to as the bottom emission type. On a substrate 201, a transparent electrode layer 202, a function layer (organic light emitting layer) 203, and a back electrode layer 205 are stacked, the layers being sealed by a sealing portion 206 (e.g., Patent Document 1).
Further, the transparent electrode layer 202 is a thin film of metal oxide or the like being stacked. The function layer 203 is made up of a plurality of thin films of organic compounds being stacked. The thickness of the function layer 203 is normally extremely small, i.e., several hundred nanometers. The back electrode layer 205 is a thin film of metal or the like being stacked.
The representative layer structure of the function layer 203 is as shown in FIG. 12. The function layer 203 includes a hole injection layer 210, a hole transportation layer 211, a light emitting layer 212, and an electron transportation layer 213. Further, an electron injection layer is inserted between the electron transportation layer 213 and the back electrode layer 205 as necessary.
That is, light emitted in the function layer (organic light emitting layer) 203 is outputted by transmitting through the lamination structure that structures the organic EL device. In this manner, the organic EL device functions as a self-luminous device.